1. Field of the Invention
The present invention relates to a sight for use in a gun or the like to guide the eyes and more particularly, to an internal red dot sight, which projects a virtual point light source onto the objective lens, simulating the parallel emission of a point light source from a remote site and, which employs coating techniques to control the percentage of red light reflection, achieving the objects of shortening the length of the internal red dot sight, increasing the size of the objective lens, reducing the manufacturing cost of the internal red dot sight, and improving the projection precision of the light source.
2. Description of the Related Art
Conventional sights for use in guns to guide the eyes include two types, namely, the internal red dot type and the external red dot type. In a battle, the sight helps the fighter to achieve fast target acquisition. A regular external red dot sight uses a laser pointer to project a laser beam directly projected onto the target, leaving a red point on the target for target acquisition. However, the location of an external red dot sight user can easily be seen. Further, when the intensity of the ambient light is high, the user may be unable to identify the red dot on the target. Internal red dot sights are developed to eliminate the aforesaid drawbacks. An internal red dot sight only uses the red (or green) dot within the sight. Because the dot is not projected to the target, the user's location will not be found, and the ambient light does not affect the presence of the dot within the sight.
FIGS. 4 and 5 show an internal red dot sight B according to the prior art. According to this design, the internal red dot sight B comprises a concave lens A having a circular arch with an angle. A centre C of the circle of the concave lens A is on the major axis, and a focal point F is on the mid point between the centre C and the concave lens A. When the red dot is projected from the focal point F to the concave lens A, the concave lens A reflects the light beam in parallel to the major axis, thereby satisfying that incident angle=angle of reflection, and therefore the user's eye can see the dot on the concave lens A that is superimposed on the target. This design is functional, however it still has drawbacks.
After installation of the internal red dot sight B in the weapon, the user must approach the eye to the concave lens A to search the reflected red dot off the concave lens A. Because only the light rays that are reflected by the convex lens A around the major axis pass in parallel to the major axis to produce a red dot, the user must aim the eye at the centre area of the concave lens A. When seeing the border area of the concave lens A, the image of the red dot becomes twisted. If the diameter of the concave lens A is made relatively smaller, the parallel light ray reflection range of the concave lens A will be relatively reduced, narrowing the effective view range. However, when increasing the diameter of the concave lens A, the distance of the focal point F will become relatively farther, and the distance between the light source and the concave lens A will also become relatively longer (see FIG. 5). In this case, the size and weight of the internal red dot sight B will be relatively increased.
There is also known an internal red dot sight that uses a laser projection technique to produce a red dot through multiple reflections of the light beam of a laser source. This design requires a precision calibration to map the red dot. Further, this design uses a big number of lenses, resulting in a high cost. If the internal red dot sight falls to the ground accidentally, the angle of reflection of the laser beam will be biased, resulting in a focusing failure. In this case, the laser beam may injure the user's eye.
Therefore, it is desirable to provide an internal red dot sight that eliminates the aforesaid problems.